Phnom Penh was abandoned for 360 years and came back to exactly the same spot.

01 Four arms of water

The Khmer name of the site, Chaktomuk, means 'four faces' or 'four arms', and it describes exactly what you see from the river promenade. Three rivers converge here: the Mekong, coming down from the north; the Tonlé Sap, arriving from the lake of the same name; and the Bassac, heading south. Out of the meeting come four stretches of water in a cross.

This is not a postcard detail, it is the reason for everything else. A point where three navigable rivers meet is a hub of transport and trade in a country with no coast in that direction, and it is also the place from which you control what enters and leaves the interior. Anyone wanting to govern this plain had to be here.

02 Sixty-three years, and then nothing

The chronology is surprisingly short in its first stretch. The city is founded in 1372 and is the capital between 1434 and 1497: sixty-three years. In 1505 it is abandoned, and from then on the capital moves elsewhere and does not return here until 1865. That is three hundred and sixty years in which the place exists but does not rule.

That gap has a practical consequence you notice on foot: there is no medieval core here. What you walk through is a city of the last century and a half, with a layout of broad avenues set out from 1865, twentieth-century buildings and a centre that has been rebuilt several times. Anyone coming for old stone has picked the wrong destination.

03 Why it came back here and nowhere else

The short answer is that there was no alternative. On an alluvial plain without relief, where the roads flood for part of the year and heavy transport goes by water, a crossing of three navigable rivers is a resource you cannot replicate twenty kilometres away. The geography here offers no second-best site.

There is a second reason too, less obvious and more interesting: the Tonlé Sap is not an ordinary river. For half the year it flows south, like any other, and for the other half it flows north, pushed by the Mekong's flood. That is, the junction does not merely distribute water: it distributes it in both directions depending on the season.

04 A city that still faces the water

Today it is a large capital: 2.35 million people in the city and almost 3.5 in the metropolitan area according to the 2019 census, across 679 square kilometres. And it is still low-lying: the mean level sits barely twelve metres above the river, which explains why the water level here is an everyday concern and not a curiosity.

The river traffic is not decorative. Convoys of barges loaded with containers pass in front of the promenade, and the port remains an economic asset of the first order. In a city where almost everything else has changed several times in a hundred years, what has not changed is what the site is for.

05 What Phnom Penh leaves you with

You come away with an unintuitive idea about how cities get made. We are used to thinking that a capital is the result of a political decision, and here you see the opposite case: the decision was taken twice, three hundred and sixty years apart and in completely different circumstances, and the result was the same point on the map.

And it leaves a very simple exercise worth doing. Sit on the promenade, watch the water for a good while and try to decide which way it is going. Depending on the month, the answer changes. There are not many cities where that question has two correct answers a year.